Telomeres are genetic elements located at the ends of all eukaryotic chromosomes which preserve genome stability and cell viability by preventing aberrant recombination and degradation of DNA (McClintock, 1941, Genetics vol 26, (2) pp 234-282; Muller, (1938) The collecting net, vol 13, (8) pp 181-198). In humans, the telomeric sequence is composed of 10-20 kilobases of TTAGGG repeats (Harley et al., 1990) Nature vol. 345 pp 458-460; Blackburn, (1991) Nature vol. 350 pp 569-573; de Lange et al., (1990) Mol. Cell Biol. Vol 10, (2) pp 518-527). There is increasing evidence that gradual loss of telomeric repeat sequences (TTAGGG) may be a timing (“clock”) mechanism limiting the number of cellular divisions in normal human cells (Allsopp et al., (1992) Proc. Natl. Acad. Sci. USA, vol. 89, pp. 10114-10118; Harley et al., (1990) Nature, vol. 345, pp. 458-460; Hastie et al., (1990) Nature, vol. 346, pp. 866-868; Vaziri et al., (1993) Amer. J. Hum. Genet., vol. 52, pp. 661-667). In contrast, immortal cells are capable of maintaining a stable telomere length by upregulating or reactivating telomerase, a ribonucleoprotein enzyme that is able to add telomeric repeats to the ends of chromosomes (Greider and Blackburn, (1985) Cell, vol. 43, pp. 405-413; Greider and Blackburn, (1989) Nature, vol. 337, pp. 331-337; Morin, (1989) Cell, vol. 59, pp. 521-529).
Telomerase is an enzyme which adds nucleotides to the telomeres at the ends of chromosomes, helping to prevent telomeric shortening to critical lengths. Structurally telomerase is a unique macromolecular complex which incorporates a strand of RNA in its active site. This RNA includes telomeric complementary sequence (3′-AUCCCAAUC-5′), which functions both to anchor telomerase to the telomere and as a template for adding repeats to the chromosome end. Telomerase is active in essentially all cancers, but is generally present at very low or non-detectable levels in normal adult tissue. Thus, the average telomere length of normal cells varies among individuals and declines with age (see FIG. 7). Telomere shortening in normal tissues may also be accelerated by oxidative, physiologic or immunologic stress and exposure to toxic agents.
Cancer cells generally undergo repeated rounds of cell division and have telomeres that are stable, but shorter than those in normal cells. Telomerase activation is necessary for most cancer cells to replicate indefinitely and thereby enables tumor growth and metastasis. (Kim et al., Science vol. 266 pp 2011-2015; Greider C W, Blackburn E H. Sci Am February: 92-97, 1996; Shay J W and Wright W E. “Senescence and immortalization: role of telomeres and telomerase” Carcinogenesis 26:867-74, 2005). Therefore inhibition of telomerase is considered a promising treatment strategy for a broad variety of solid tumor types and hematological malignancies (Harley C B, Nature Rev. Cancer, vol. 8 pp 167-179, 2008).
GRN163L is a thio-phosphoramidate oligonucleotide with a 5′ palmitoyl “tail”. It inhibits the activity of intracellular telomerase by binding to the template region of the RNA component of the telomerase holoezyme. (Shea-Herbert et al Oncogene 24:5262-8, 2005) GRN163L has demonstrated telomerase inhibition and cancer cell growth inhibition effects both in vitro and in vivo (Dikmen Z G, et al. Cancer Res. 65:7866-73, 2005; Djojosobruto M W et al. Hepatol 42:1-11, 2005; Hochreiter A E, et al. Clin Cancer Res 12:3184-92 2006) GRN163L is currently in clinical trials in solid tumor and hematological cancers.
In any cancer treatment, chemotherapy-induced toxicity can result in reductions in relative dose intensity of the chemotherapy. Treatment-induced toxicities can include anemia, neutropenia, leucopenia and thrombocytopenia. Thrombocytopenia is a chemotherapy-induced toxicity that typically occurs in the first round of chemotherapy treatment and may become more severe during repeated rounds of treatment. Drugs that result in toxicities may have limited applications because of reduced dose intensity (RDI), dose delays and relative dose reductions. Such dose reductions, reduced dose intensity or dose delays used as a means of reducing toxicity may undermine disease control and overall survival, particularly in patients with potentially curable malignancies. It is generally recommended that in order to gain maximum benefit-risk ratio from chemotherapy, the dose prescribed should be individualized according to the goal of therapy and response.
Treatment of thrombocytopenia is determined by the etiology and disease severity. The main concept in treating thrombocytopenia is to eliminate the underlying problem, whether that means discontinuing suspected drugs that cause thrombocytopenia, or treating contributing immunologic or inflammatory factors. Patients with severe thrombocytopenia may be managed with transfusions of donor platelets for a period of time. In addition, Oprelvekin (NEUMEGA™, Wyeth) is approved for the prevention of severe thrombocytopenia following myelosuppresive chemotherapy in adult patients with nonmyeloid malignancies. Another drug, Romiplostin (NPLATE™, Amgen Inc.) has been approved for the treatment of chronic idiopathic thrombocytopenic purpura (ITP).
In this context, a highly predictive test for patients who are sensitive to developing telomerase inhibition therapy-induced toxicity would provide significant reduction in the total burden of toxicity associated with telomerase inhibition therapy, and allow for the safer use of telomerase inhibition therapy without inappropriate denial of access to its use.
The present invention seeks to present a method for determining the susceptibility of cancer patients to developing treatment limiting toxicities, such as thrombocytopenia, from telomerase inhibition therapy.